knitr::opts_chunk$set(fig.width=6, fig.height=4)
Nutrient enrichment is recognized as a major threat to biodiversity worldwide
Question of scale - constant problem in ecology.
Much of our understanding of how nitrogen enrichment impacts plant diversity comes from small-scale experiments - responses observed in a 1m2 plot or smaller
Extrapolating from the results of these small-scale experiments to broader patterns comes with some caveats
Many ecological phenomena exhibit scale-dependence, particularly with respect to spatial scale of sampling
Because many experiments evaluate effects at a single spatial scale, you’re likely to miss nuanced interpretation that can produce meaningful insights into how different environmental stressors impact plant diversity.
Nutrient enrichment (particularly nitrogen) is a highly pervasive environmental stressor
Fertilization increases plant growth and intensity of light competition that favors large, fast growing species
Notion of niche collapse - addition of a limiting nutrient reduces relevant variation in its contribution to species fitness
Therefore, addition of multiple limiting nutrients can have greater effects than saturation of a single resource
When resources are spatially heterogeneous, nutrient addition can act as a homogenizing force
High plant diversity, despite invasive history
High spatial heterogeneity of vegetation and soil resources
To quantify spatial scale-dependence, classic approaches utilze species-accumulation curves which relate observed diversity to sampling effort.
We can use these curves to determine how effects vary with scale, and identify whether effects increase or decrease with spatial scale, as well as inflection points where interpetation flips.
However, when species accumulation curves are composed of individual sampling subunits, we can also vary the way in which we accumulate diversity (spatially or randomly) - detecting the influence of spatial processes on the shape of this relationship, such as spatial aggregation (clustering of individuals)
Show two communities - one with a greater number of species at the gamma scale and lower species richness per sample unit + aggregation, one with a smaller number of species at the gamma scale and lower species richness per sample unit + no aggregation.
Demonstrate the steps to my analysis (borrowing elements of the analysis framework of McGlinn et al. (2018)):
Alpha, gamma, and beta diversity - the endpoints of this relationship
Spatial accumulation order + its resulting curve
Random accumulation order + its resulting curve
Mean difference in these curves (aggregation effect in each community)
Relative contribution of aggregation effect to the shape of this scaling relationship (net change)
Do nutrient enrichment effects vary with spatial scale?
Does use of abundance weighted metrics change our interpretation of effects?
How does spatial aggregation contribute to the observed differences between curves?
Plant biomass change
Light availability change
Community composition
Biomass change over time
Light availability change over time
Light Meter Readings.
2017 Species Richness Accumulation
2017 Effective Number of Species Accumulation
2018 Species Richness Accumulation
2018 Effective Number of Species Accumulation
Alpha Change.
Beta Change.
Gamma Change.
Net effect over scales (nonlinear patterns for Q = 0, more linear patterns for Q = 2)
Change in net effect (greater effect at intermediate scales than otherwise)
Species richness aggregation effect
ENSpie aggregation effect
Individual density? Much of this spatial scaling work delves into the role of number of individuals in diversity patterns (particularly important in invasive work?), but also may be important in situations where increased nutrient availability increases individual size and reduces packing efficiency.
Knowing that blocks are the same + sampling design? Be good to mention briefly in methods or be prepared to have more detail in afterword that notes how we chose the sampling grain and extent - variation in quadrat area and spatial lag.